Method of manufacturing a seal and restraining system

ABSTRACT

A method and apparatus for restraining pipe against both internal and external forces at a pipe or fitting connection and to join and seal at least two pipes to form a pipeline is shown featuring an improved restraining and sealing mechanism. The restraining and sealing mechanism includes a circumferential housing and a companion sealing ring which are received within a mating groove provided in the belled end of a female pipe. The circumferential housing has an interior region which contains a gripping ring insert. The sealing ring and housing are integrally located within a belled pipe end during belling operations.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from earlier filed provisionalapplication Ser. No. 60/633,888, filed Dec. 7, 2004, entitled“Combination Seal and Restraint System for Plastic Pipe,” by Bradford G.Corbett, Jr., and Jim Jones.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of pipeconnections, and in particular, to a dual function, self restrainingsealing system that is used to form a secure pipe connection between twoplastic pipes and to a method of manufacturing the same.

2. Description of the Related Art

Pipes are commonly used for the conveyance of fluids under pressure, asin city water lines. They may also be used as free-flowing conduitsrunning partly full, as in drains and sewers. Pipes for conveying waterin appreciable quantities have been made of steel, cast iron, concrete,vitrified clay, and most recently, plastic including the variouspolyolefins and PVC.

It is well known in the art to extrude plastic pipes in an elongatedcylindrical configuration of a desired diameter and to then cut theextruded product into individual lengths of convenient size suitable forhandling, shipping and installing. Each length of pipe is enlarged or“belled” at one end sufficiently to join the next adjacent pipe sectionby receiving in the female, belled end the unenlarged or “spigot” maleend of the next adjacent length of pipe. The inside diameter of the bellis formed sufficiently large to receive the spigot end of the nextsection of pipe with sufficient clearance to allow the application ofpacking, caulking, elastomeric gaskets or other sealing devices designedto prevent leakage at pipe joints when a plurality of pipe lengths arejoined to form a pipeline.

During a standard installation of a pipeline, in, for example, municipalinstallations, the joints between pipes and between pipes and fittingsmust be restrained to accommodate varying pressures as well asenvironmental influences. For example, there are various types offitting connections which are commercially available and which are usedin, for example, the waterworks industry. In one type of connection, thecurrent restraint mechanism is an external clamping device which istotally separated from the sealing function. Thus, a separate mechanismmust perform the sealing function. In another type of fittingconnection, a gasket performs the sealing function. However, it isnecessary that an external means must compress the gasket by mechanicalaction such as T-bolts. Most current restraining systems offered in theindustry require a substantial amount of labor to install. Under mostinstallation conditions, the restraining systems are cumbersome toinstall and represent a substantial additional effort for thecontractor. As a result, these and other traditional restrainingmechanisms of the prior art add considerable cost and complexity to thepipe installation as well as adding the possibility of human errordepending upon the specific field conditions and applications.

In the early 1970's, a new technology was developed by Rieber & Son ofBergen, Norway, referred to in the industry as the “Rieber Joint.” TheRieber system provided an integral sealing mechanism within the belledor female pipe end for sealing with the spigot end of a mating pipeformed from thermoplastic material. In the Rieber process, theelastomeric gasket was inserted within an internal groove in the socketend of the female pipe as the female or belled end was simultaneouslybeing formed. The provision of a prestressed and anchored elastomericgasket during the belling process at the pipe factory provided animproved socket end for a pipe joint with a sealing gasket which wouldnot twist or flip or otherwise allow impurities to enter the sealingzones of the joint, thus increasing the reliability of the joint anddecreasing the risk of leaks or possible failure due to abrasion. TheRieber process is described in the following issued United Statespatents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872;3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682. While theRieber process provided an improved sealing system for plastic pipelinesof the type under consideration, it did not include any integralrestraint type mechanism.

Accordingly, there is a need for a cost-effective, easy to manufactureand use combination seal and restraint system for restraining andsealing plastic pipe against internal and external forces at a pipe orfitting connection and for joining and sealing at least two plasticpipes at a pipe joint to form a pipeline.

There also exists a need for such a sealing and restraint system inwhich the restraint mechanism is integral to the groove formed in thebell end opening of a female pipe member which member receives a matingmale, spigot pipe end to form a pipe joint in a fluid conveyingpipeline.

There is also a need for such a combination seal and restraint system inwhich the restraint portion of the system works independently of theseal and can accept differing seal profiles.

There also exists a need for such a combination seal and restraintsystem in which the seal portion works in complimentary fashion toenhance the action or energize the restraint portion of the mechanism.

There exists a need for such a seal and restraint system having allinternal components so that problems with corrosion of external metalliccomponents are eliminated.

There exists a need for such a seal and restraint system which iscomprised of components which can be mounted on a forming mandrel andwhich can be belled over in a Rieber style manufacturing operation.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a seal andrestraint system in which the restraint mechanism is integral to thegroove formed in the bell end opening of a female pipe member whichmember receives a mating male, spigot pipe end.

It is a preferred object of the invention to provide an improved sealand restraint system for plastic pipe joints utilizing a Rieber style“gasket formed” bell groove, which does not require assembly in thefield and which thus simplifies installation of pipe sections at thepipe joints used to form a fluid conveying pipeline, thereby reducingthe chance of human error or of damage or contamination of the gasketsealing surfaces.

Another object is to eliminate the need for an external clamping deviceof the type presently used in the industry to achieve the restrainingfunction, which device is totally separated from the sealing functionand which typically utilizes metallic components which are subject tocorrosion over time.

Another object of the present invention is to provide an improvedrestraint system for plastic pipe which is simple in design anddependable in operation and which is less costly in terms of bothmaterials and labor than the restraining systems presently employingexternal mechanical restraints.

In the method and apparatus of the invention, an integral bellpipe-to-pipe seal and restraint system is provided for restraining pipeagainst internal or external forces at a pipe coupling or fittingconnection and for joining and sealing at least two pipes to form apipeline. The seal and restraint system of the invention utilizes anelastomeric sealing ring in conjunction with a special cooperatingrestraint mechanism. The restraint mechanism is designed to workindependently but in complimentary fashion with the seal and can acceptdifferent seal profiles. Alternatively, the seal and the restraintmechanism may be bonded or otherwise formed together so that they arehandled as a single piece. The bonding may be intentionally weak so thatthe seal detaches from the restraint mechanism during the bellingoperation or during use.

In a particularly preferred form of the invention, the restraintmechanism includes a ring shaped housing having a circumferentialhousing interior. The ring shaped housing is positioned on the exteriorof a forming mandrel and the pipe bell end is formed over the housing ina Rieber style belling operation. A companion ring-shaped grippinginsert is provided which can be installed and contained within acircumferential region provided in the housing interior. The ring-shapedgripping insert preferably has at least one circumferential slit in thecircumference thereof which allows it to be installed after the femaleplastic pipe end is belled over the housing. The ring is temporarilycompressed and snapped or popped within the circumferential regionprovided in the housing interior. The gripping insert also has one ormore rows of gripping teeth on an interior surface thereof.

Alternatively, the gripping insert can be installed within the housingas a part of the belling operation with a removable spacer beingtemporarily placed in the circumferential slit in the gripping insert,whereby the gripping insert is spread apart an additional, preselectedamount. The housing and gripping insert are then installed on theforming mandrel. The amount of spacing is selected to cause the grippinginsert to be initially received more closely within the housing interiorregion, whereby the teeth of the gripping insert are concealed in thehousing interior region and do not make detrimental contact with anassociated forming mandrel during the belling operation.

Using the latter technique, both the seal and the restraint mechanismare loaded onto a forming mandrel, typically at a receiving groove onthe mandrel exterior. The heated pipe end of a female plastic pipe isforced over the mandrel exterior and, in turn, over the seal and housingof the restraint mechanism. The heated pipe end is then cooled and thebelled pipe end containing the housing and gripping insert is withdrawnfrom the forming mandrel. The removable spacer may remain in position inthe gripping insert during storage of the belled pipe end. The spacer istypically removed before the assembly of a pipe joint in the field inorder to activate the restraining mechanism. The spacer may also beintentionally left in place to deliberately disable the restraintmechanism.

Since the female end of the plastic pipe is belled around the seal andat least the ring shaped housing of the restraining mechanism, therestraint system is integral with the bell. In this way, it is notnecessary to install the restraint system in the field and, since thesystem is also locked in position at the factory by means of the bellingoperation, it is less likely to be dislodged or twisted during assemblyof the pipe joint.

In the preferred embodiment of the invention, the plastic pipe is madeof PVC. The preferred materials for the ring shaped housing and grippingring insert include materials selected from the group consisting ofmetals, composites and rigid elastomers or plastics. The preferredsealing ring is formed from a material selected from the groupconsisting of natural and synthetic rubbers and elastomers, polymericplastics and composites. The spacer for the gripping ring is preferablyformed of a suitable plastic.

The above as well as additional objectives, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly broken away, of male and femalepipe sections about to be made up into a pipe coupling, the belled endof the female pipe section showing one embodiment of the seal andrestraint mechanism of the invention in place within a mating grooveprovided therein.

FIG. 2A is a side, cross-sectional view of a portion of the female pipesection showing the seal and restraint system of FIG. 1 in greaterdetail.

FIG. 2B is a view similar to FIG. 2A, but showing the beginning step ofinserting the male pipe section within the female, belled pipe end, themale and female pipe sections being joined to form a secure connection.

FIGS. 3-6 are simplified, schematic views of the prior art Rieberprocess used to form the female belled pipe end.

FIG. 7 is an enlarged, side cross-sectional view of the seal andrestraint system of the invention showing certain aspects of thegeometry thereof.

FIG. 8 is an isolated view of the gripping insert which is receivedwithin the circumferential interior region of the housing in therestraint system of the invention.

FIG. 9 is a top view of the gripping insert of FIG. 8 showing the slitin the circumference thereof and showing a removable spacer about to befitted within the gap.

FIG. 10 is a side, partially schematic view of one version of a formingmandrel used with the seal and restraint system of the invention.

FIG. 11 is a close-up view of a portion of the mandrel of FIG. 10showing the collapsible surfaces thereof.

FIG. 12 is a side, cross-sectional view similar to FIG. 2A, but showingan alternate ring shaped housing and gripping insert of the invention.

FIG. 13 is an isolated cross-sectional view of the gripping insert ofFIG. 12.

FIG. 14 is a top view of the gripping insert of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning to FIG. 1, there is shown an exploded view of a plastic pipejoint in which a belled female pipe end 10 is provided with an annulargroove (shown as 12 in FIG. 2A) for receiving the seal and restraintmechanism 14 of the invention. The improved integral seal and restraintmechanism of the invention is capable of joining and sealing the femaleplastic pipe 10 to the spigot end of a mating male plastic pipe section20 having an exterior surface 24. The plastic pipe male and female ends10, 20 can be made from any convenient synthetic material including thepolyolefins such as polyethylene and polypropylene but are preferablymade from polyvinyl chloride (PVC).

As best seen in FIGS. 1, 2A and 2B, the seal and restraint mechanism 14includes an elastomeric, circumferential sealing ring 16 which is formedas an elastomeric body. The annular sealing ring 16 is somewhat teardrop shaped in cross section and includes a bulbous end region 28 (FIG.2A) and a thinner forward most region 30. The bulbous end region 28terminates in a nose portion 8. The sealing portion also has an exposedexterior region (generally at 32) which contacts the exterior surface 24(FIG. 2B) of the mating male pipe section upon assembly of the joint.The sealing member is preferably made of a resilient elastomeric orthermoplastic material. The sealing member can be formed, for example,from natural or synthetic rubber, such as SBR, or other elastomericmaterials which will be familiar to those skilled in the plastic pipearts such as EPDM or nitrile rubber. In this case, the sealing ring 16has a metal reinforcing band 17 about the outer circumference thereof.However, as will be apparent from the description which follows, anynumber of specialized sealing rings can be utilized in order to optimizethe sealing and restraining actions of the assembly.

The seal and restraint system of the invention also includes a companionrestraint mechanism for the sealing ring 16 which allows movement of themating male pipe (20 in FIG. 1) relative to the belled end of the femalepipe 10 in a first longitudinal direction but which restrains movementin a second, opposite relative direction. The companion restraintmechanism includes a ring shaped housing 18 (FIG. 2A) having acircumferential interior region 19 and an exterior 21. The ring shapedhousing provides radial stability and reinforcement for the male(spigot) pipe end during make up of the joint so that the male pipe end20 is radially supported and remains perfectly circular during the jointassembly process. The exterior 21 extends from a nose region 22 (FIG.2B) in convex fashion, gradually flattening out into a planar backregion which terminates in a tip region 24. The tip region 24 serves asa protective skirt which covers any gap between the sealing ring 16 andring shaped housing 18 during the pipe belling operation. Although thehousing could have a circumferential opening, it is preferably providedas a solid ring of a slightly larger internal diameter than the formingmandrel (to be described) upon which it is received during pipe bellingoperations. Alternatively, the housing could be used with some form ofcollapsible forming mandrel, in which case its internal diameter mightapproach or exceed that of the mandrel in certain of its states ofoperation. The exterior 21 of the housing 18 may be equipped with one ormore rows of gripping teeth 23 for engaging the surrounding pipe groove12. The corresponding grooves or indentations in the pipe interior wouldbe formed during the belling operation as the pipe cools. The ringshaped housing 18 is preferably formed of a material selected from thegroup consisting of metals, alloys, elastomers, polymeric plastics andcomposites and is rigid or semi-rigid in nature.

The leading portion of the circumferential interior region 19 is slopedupwardly with respect to the longitudinal axis (25 in FIG. 1) of thepipe. This leading portion 19 forms an upwardly sloping ramp surface fora companion gripping insert 27. The sloping ramp surface extendsupwardly from a positive stop region (34 in FIG. 2B) and graduallyflattens into a planar circumferential region which terminates in aninternal shoulder (26 in FIG. 2B) arranged opposite an external shoulder44. The positive stop region 34 prevents the companion gripping insert27 from overly compressing the O.D. of the mating male pipe as the pipejoint is being assembled.

The housing external shoulder (44 in FIGS. 2A and 2B) is substantiallyperpendicular to the longitudinal axis 25 of the female pipe. Theexternal shoulder 44 is in contact with the nose region of theelastomeric body of the sealing ring 16 as the mating male pipe isinserted into the mouth opening (46 in FIG. 1) of the female belled pipeend 10. The housing and sealing ring can be provided as separate pieces,as shown in FIGS. 2A and 2B, or can be at least temporarily joined at ajuncture point prior to the pipe belling operation. For example, asuitable glue or adhesive could be used to form a temporary juncture atthe external shoulder 44 of the housing 18. In such case, the temporaryjuncture would typically be designed to be severed during the bellingoperation so that the sealing ring 16 and the housing 18 are separate atthe time a pipe joint is made up in a field application. The housing 18could also be integrated with the sealing ring 16, as during the curingof the elastomeric body of the ring.

FIGS. 2A and 2B illustrate the positioning of the companion ring-shapedgripping insert 27 which is received in complimentary fashion andcontained within the circumferential interior region 19 of the housing18. As shown in FIGS. 2A and 2B, the nose region 22 of the grippinginsert 27 contacts the positive stop region 34 on the I.D. of thehousing 18 in the forward most position to thereby assist in retainingthe gripping insert within the housing. The gripping insert 27 has anexterior surface 31 (FIG. 8) and an interior surface 33 with at leastone row of gripping teeth 35. In the embodiment of the invention shownin FIG. 8, the gripping insert 27 has four rows of teeth 35, 37, 39 and43. The rows of teeth are arranged for engaging selected points on theexterior surface 24 of the mating male pipe section 20.

The gripping insert exterior surface 31 has a sloping profile (42 inFIG. 8) which contacts the upwardly sloping ramp surface (generally at19 in FIG. 2A) of the housing 18, whereby contact with the exteriorsurface of a mating male pipe (20 in FIG. 2B) causes the gripping insert27 to ride along the male pipe exterior surface at an angle while therow of gripping teeth on the gripping insert internal surface engage theexterior surface of the mating male pipe.

The rows of teeth 35, 37, 39, 43 on the lower surface 33 of the ringshaped insert 27 can be of equal length or can vary in length and can bearranged in either a uniform or non-uniform pattern about the innercircumference of the gripping insert. The teeth of the gripping insertare also angled away from the horizontal axis of the joint (25 in FIG.7) at an angle “α” of less than 90°.

As best seen in FIG. 9, the gripping insert has at least one slit 37 inthe circumference thereof which forms an opening of approximately 15°with respect to the central axis 39, as viewed in FIG. 9, for theparticular size insert in question. The gripping insert 27 is a rigid orrelatively rigid member. By “relatively rigid” is meant that thegripping insert 27 can be formed of a hard metal, such as corrosionresistant stainless steel, or from other metallic materials or alloys oreven a hardened plastic or composite.

FIGS. 12-14 illustrate another version of the housing and grippinginsert of the invention. The ring shaped housing 55 in FIG. 12 again hasa circumferential interior region 57 and an exterior 59. The exterior 59extends from a nose region 61 in convex fashion, gradually flatteningout into a planar back region which terminates in a tip region 63.Unlike the housing 18 shown in FIG. 2A, the housing 55 of FIG. 12 hasthe rows of exterior teeth 65 all moved forward of a central verticalaxis 67. The placement of the teeth 65 has been found to moreeffectively counteract the opposing force of the pressurized pipe in usewhich would otherwise tend to cause the pipe joint to be forced apartand to cause the restraint mechanism to be squeezed through theresulting gap. The space indicated generally at 69 in FIG. 12 isintended to illustrate that the preferred gripping ring insert 71 is nowdramatically smaller in diameter than the male spigot pipe end. Thisdifference in ring diameter effectively means that the male spigot pipeend must expand the gripping ring insert 71 as the pipe joint is beingassembled. As a result, there is some drag on the pipe exterior duringinstallation which facilitates the biting and gripping action of thegripping insert teeth 73.

As shown in FIG. 12, the housing circumferential interior region 75again slopes upwardly with respect to the pipe longitudinal axis withthe leading portion thereof forming an upwardly sloping ramp surface fora companion ring shaped gripping insert 71. The sloping ramp surfaceextends upwardly from a positive stop region (77 in FIG. 12) andgradually flattens into a planar circumferential region which terminatesin an internal shoulder 79 arranged opposite external shoulder 81. Thepositive stop region 77 prevents the gripping insert ring 71 fromtending to over-compress the mating male plastic pipe section duringassembly of the pipe joint. As a result of the interaction of thegripping insert ring 71 and the stop region 77, there is no pointloading or pipe distortion during assembly. While point loading may notbe a significant factor in ductile iron systems, it can be a criticalfactor in ductile iron to plastic systems.

FIG. 13 illustrates the different geometry of the gripping ring insert71. As will be apparent from the cross-section, the gripping insert 71has a generally rectangular cross-sectional region 83 to the rear of avertical axis 85 and a conically shaped cross-sectional leading region87 forward of the axis 85. The O.D. of the insert 71 has a sloping noseregion 89 which joins a cylindrical outer surface 91. The interiorcircumference 88 has a plurality of rows of gripping teeth, such as row93 in FIG. 13. In the embodiment of the device illustrated in FIG. 13,the rows of teeth are evenly spaced and the height of the teeth(indicated as “h” in FIG. 13) in each row is identical. As best seen inFIG. 14, the gripping insert has at least one slit 95 in thecircumference thereof which forms an opening of approximately 15° withrespect to the central axis 97, for the particular size insert inquestion.

The modified design of the gripping insert 71 tends to concentrate thecontact force during assembly of the pipe joint on the leading teeth (93in FIG. 13). As the teeth begin to sink into the exterior surface of themating male pipe, the insert tends to recover its original posture, sothat all of the rows of teeth tend to produce the same indentation. Byusing the ring geometry shown in FIG. 13 and by increasing theinterference between the ring and the male pipe (by decreasing thediameter of the gripping insert), contact force can be concentrated onthe leading row of teeth 93, even where all the rows of teeth are of thesame size or height. As a result, once the gripping portion of therestraint mechanism is activated, all of the teeth have virtually thesame penetration into the male pipe.

Because the preferred restraint system of the invention utilizes twocomponents, namely the sealing ring and the rigid gripper ring, thesealing ring can actually serve to pre-load or energize the gripper ringso that the ring is more firmly engaged on the exterior surface of themale pipe section. This can be accomplished, for example, byintentionally providing an excess amount of rubber in the sealing ringover that normally provided to perform the sealing function alone sothat the sealing ring bears against the gripper ring and creates apositive loading effect.

FIGS. 1, 2A and 2B also illustrate the make-up of a joint of plasticpipe in which the male spigot end 20 is inserted within the belledfemale pipe section 10. FIG. 2B illustrates the gripping action of therows of teeth 35, 37, 39, 43 of the gripping insert in which the teethgrip the exterior surface 24 of the male pipe section 18. The rows ofteeth 35, 37, 39, 43 are angled inwardly with respect to the axis 25 sothat contact with the male pipe end (20 in FIG. 2B) causes the teeth tobe deflected in a counterclockwise direction with respect to axis 25during the insertion step, as viewed in FIG. 2B. Once the male pipesection 18 has been fully inserted, the rows of teeth 35, 37, 39, 43grip the exterior surface of the male pipe and resist movement in anopposite longitudinal direction. The nose region 8 of the sealing ring16 also contacts and forms a sealing region with respect to the externalshoulder 44 of the housing 18.

In order to explain the manufacturing process used to locate the sealand restraint system of the invention within the mating groove providedin the female pipe end 10, it is necessary to briefly explain the priorart “Rieber” process for plastic pipe manufacture. That was brieflydescribed in the Background of the Invention. As previously described,in the Rieber process, the elastomeric gasket was installed within asimultaneously formed internal groove in the socket end of the femalepipe during the pipe belling process. The provision of a prestressed andanchored elastomeric gasket during the belling process at the pipefactory provided an improved socket end for a pipe joint with a sealinggasket which would not twist or flip or otherwise allow impurities toenter the sealing zones of the joint, thus increasing the reliability ofthe joint and decreasing the risk of leaks or possible failure due toabrasion.

While the Rieber process provided an integral sealing gasket which was“prelocated” within the belled, female pipe end in a groove which wasformed about the gasket, it did not provide any mechanical “restrainingfunction” to prevent separation of the male and female pipe ends at thepipe connection once the pipe joint was made up.

The relevance of the Rieber process to Applicant's invention can perhapsbest be appreciated with reference to the description of the prior artprocess shown in FIGS. 3-6. FIG. 3 shows a section of a conventionalelastomeric sealing gasket 111 having a steel reinforcing ring 113 inplace on the generally cylindrical outer working surface 115 of themandrel 117 used in the belling process. The elastomeric gasket 111 canbe formed of, for example, SBR rubber and is a ring shaped,circumferential member having an inner compression surface 119 and anexposed nose portion 121 which, as shown in FIG. 3, abuts a formingcollar 123. The forming collar 123 has a first generally cylindricalextent 125 which is joined to a second cylindrical extent 127 by a stepregion 129, whereby the second extent 127 is of greater externaldiameter than the first cylindrical extent 125, shown in FIG. 3.

In the first step of the prior art process, the steel reinforcedelastomeric ring 111 is thus placed onto the working surface of themandrel 117 and pushed to a position against the back-up or formingcollar 123. In this position, the gasket is firmly anchored to themandrel surface with the rubber between the mandrel and the steel-ringof the gasket being compressed by approximately 20%.

In the second step of the prior art process, the socket end 133 of thethermoplastic pipe 131 is heated and pushed over the steel mandrel 117,gasket 111 and back-up collar 123. The socket end 133 is expanded due tothe thermoplastic nature of the pipe. A number of thermoplasticmaterials, such as polyethylene, polypropylene and polyvinylchloride(PVC) are known in the prior art having the required expansioncharacteristics, depending upon the end application of the pipe joint.However, the preferred material for this application is PVC due to itsexpansion and contraction characteristics. The socket end 133 flows overthe first cylindrical extent 125 of the back-up collar 123 and abuts thestep region 129 in the second step of the process. Note that the pipeend is deformed by the presence of the gasket 11 so that a gasketreceiving groove is formed with the pipe I.D.

In the next step of the prior art process (FIG. 5) the mandrel and pipemove away from the back-up collar 123 and the pipe socket end 133retracts around the mandrel and gasket 111 due to the elastic forces ofthe thermoplastic material. Typically, vacuum was also applied throughports 135, 137 which connected the mandrel working surface with a vacuumsource (not shown). In the final step of the prior art process, the pipesocket end 133 is cooled by means of a water spray bar 139 and spraynozzles 141. As the cooling takes place, the pipe socket end 133 shrinksaround the gasket 111, thus compressing the rubber body of the gasketbetween the steel reinforcing ring 113 and the socket-groove toestablish a firm seal. The above described Rieber process has been incommercial use since the early 1970's and is described in the abovereferenced issued United States patents, among other sources. It willthus be well familiar to those skilled in the thermoplastic pipe sealingarts.

Applicant's seal and restraint mechanism differs from the abovedescribed Rieber process in that the system of the invention serves toprovide both sealing and restraining functions. In the preferredembodiment, the system is comprised of two distinct components, thepreviously described sealing ring 16 and the housing 18 and companiongripping insert 27, rather than a single elastomeric component.

The method of installing the components of the restraining system of theinvention will now be described. In the preferred method ofinstallation, the sealing ring (16 in FIG. 2A) and ring shaped housing18 are placed side by side on the forming mandrel (such as mandrel 117in FIG. 3) and the female pipe end is heated and belled over thesecomponents in the normal fashion, as has been described with respect tothe Rieber process. The backup collar position or the mandrel seatinggroove location and size may have to be adjusted for the resultingchanges in bell dimensions, i.e., to allow enough room for the housing18. Once the belled pipe end has been cooled and the forming mandrel hasbeen retracted, the gripping insert 27 can be snapped or popped intoposition on the inner circumference of the housing 18, as shown in FIG.2A.

It may also be possible to bell the female pipe end over the housing 18with the gripping insert ring 27 already,in place on the innercircumference of the housing 18. For example, a removable spacer 41 inFIG. 9 can be temporarily placed in the circumferential slit 37 in thecircumference of the gripping insert 27 once the insert has beeninstalled in the housing. In this way, the ring shaped insert is spreadapart an additional, preselected amount once the insert is receivedwithin the circumferential interior region 19 of the housing 18. As atypical example, for a ring shaped insert 27 in FIG. 9 having aninternal diameter of about 348 mm, the insertion of the spacer 41 opensthe 15° opening 37 out to about a 21° opening. At the same time, thegripping insert 27 is pushed deeper into the interior region 19 of thehousing 18. The amount the gripping insert 27 is spaced apart isselected to cause the gripping insert to be initially received moreclosely within the housing circumferential interior region 19, wherebythe teeth 35 of the insert are initially concealed in the housingcircumferential interior region 19. This placement of the spacer 41 inthe slit or opening 37 helps to prevent the insert from makingdetrimental contact with an exterior surface of a forming mandrel duringsubsequent belling operations.

Thus, it may be possible, in some circumstances, to bell the female pipeend about the seal and restraint system as described in FIGS. 3-6 byusing the previously described removable spacer 41. However, because theseal and restraint system of the invention includes two component parts,namely the resilient sealing ring and the companion rigid housing andgripping insert, it may not be possible to easily slide the companioncomponents over the belling mandrel exterior surface as in thetraditional “Rieber style” manufacturing process. The presence of therigid housing 18 may also necessitate that more specialized designfeatures be incorporated into the forming mandrel, such as the use of a“collapsible mandrel.”

FIGS. 10 and 11 illustrate, in simplified fashion, an alternativeinstallation operation in which a working mandrel is provided with anouter, generally cylindrical working surface 55 and collapsible elements48. The components 16, 18 can be positioned on the forming mandrel bytemporarily collapsing the elements 48. Once the components are inposition, the elements 48 are extended. After the heated pipe end isforced over the mandrel and expanded over the seal and restraintcomponents 16, 18, the pipe end is cooled. The mandrel elements arecollapsed inwardly by means of the actuating mechanism 50 and themandrel is then removed from the pipe. FIG. 11 is intended to illustratethe relative movements of the mandrel elements 48, in simplifiedfashion. Pipe forming mandrels featuring collapsible elements are knowngenerally by those skilled in the pipe forming arts. For example, seeU.S. Pat. No. 4,239,473 for an example of a collapsible mandrel and U.S.Pat. No. 4,643,658 for an example of a “ramp” style forming mandrel.

Because the pipe joints of the invention incorporate both a sealingmember and a separate gripping member, they depart from the teaching ofthe prior art Rieber belling process. However, as in the Riebermanufacturing process described above, the preferred seal and restraintmechanism of the invention is integrally belled in the female pipe endduring manufacture of the bell end. Thus, the seal and restraintmechanism of the invention can be installed and prelocated within amating pipe groove in the “Rieber style”, with the exception that it maybe necessary to use a “collapsible mandrel” or a “ramp” style mandrel toaccommodate the housing or gripping insert which are positioned on theexterior of the forming mandrel in some circumstances. Also, while theinvention has been described with reference to a single internal grooveformed within the female bell pipe end, it will be understood that twoor more grooves can be formed in the bell pipe end, either mechanicallyat the factory prior to installing the restraining system components, orin the Rieber fashion so that the grooves are simultaneously formedabout the restraining system positioned on the forming mandrel.

An invention has been provided with several advantages. The presentinvention provides a sealing and restraint system in which the restraintmechanism is integral to the groove formed in the bell end opening of afemale pipe member. The restraining mechanism may be provided as a partof a “gasket formed” bell groove, as in a Rieber style pipe bellingoperation where the groove is simultaneously formed as the bell pipe endis formed. In its most preferred form, the manufacturing method anddevice of the invention provide an improved seal and restraint systemfor plastic pipe joints utilizing the “gasket formed” bell groove, whichdoes not require assembly in the field and which thus simplifiesinstallation of pipe sections at the pipe joints used to form a fluidconveying pipeline.

The integral restraint system of the invention eliminates the need foran external clamping device of the type presently used in the industryto achieve the restraining function, which device is totally separatedfrom the sealing function. This eliminates the possibility of externalcorrosion of the metallic components of the prior art externalrestraints. The system of the invention is also simple in design,dependable in operation, and is less costly to manufacture than theprior art restraining systems which utilize external glands andmechanical restraint components. Because the ring components of therestraint system of the invention are pre-installed, the possibility ofmistakes during field assembly is virtually eliminated. Also, thegripping insert component of the invention applies more pressure to theexterior surface of the mating male spigot pipe end as internal pressurebuilds within the fluid coupling. This action helps to ensure theintegrity of the joint. In addition, the gripping ring component aids insealing the joint by keeping a constant gripping pressure on the malepipe end at even the lowest operating pressures of the pipeline.

While the invention has been shown in only one of its forms, it is notthus limited but is susceptible to various changes and modificationswithout departing from the spirit thereof.

1. A method of manufacturing a seal and restraining system for joiningand sealing a male plastic pipe to a mating female belled pipe end, themethod comprising the steps of: providing a forming mandrel having aninner end and an outer end and having an outer working surface; locatinga sealing ring and a companion ring shaped housing at a firstcircumferential position on the outer working surface of the mandrel,the ring shaped housing having a circumferential interior region;forming a belled pipe end about the sealing ring and companion ringshaped housing; and wherein a ring shaped gripping insert is installedin the circumferential interior region of the housing, the grippinginsert having an interior gripping surface with at least one row ofgripping teeth for engaging an exterior surface of the male plasticpipe.
 2. The method of claim 1, wherein the ring shaped gripping insertis provided with at least one circumferential slit in the circumferencethereof which allows the gripping insert to be temporarily compressedand installed within the circumferential interior region of the housingin snap-fit fashion after the ring shaped housing has been integrallyinstalled within the belled pipe end during manufacture of the femalepipe.
 3. The method of claim 1, wherein the ring shaped gripping insertis provided with at least one circumferential slit in the circumferencethereof and wherein a removable spacer is temporarily placed in thecircumferential slit in the gripping insert, whereby the gripping insertis spread apart an additional, preselected amount once the insert isreceived within the circumferential interior region of the housing. 4.The method of claim 3, wherein the gripping insert is located on theinterior surface of the housing and is spread apart a preselectedamount; wherein the housing containing the gripping insert and thecompanion sealing ring are located on the outer working surface of themandrel; wherein the belled female pipe end is formed by first heating afemale end of the plastic pipe and then forcing the heated female pipeend over the working surface of the mandrel and over the seal andcompanion housing, whereby the heated female end of the plastic pipeflows over both the seal and the housing to form a retention groove forthe seal and housing; and thereafter cooling the female pipe to form abelled pipe end followed by retracting the belled pipe end with itsretained sealing ring and housing from the working surface of themandrel.
 5. The method of claim 4, wherein the amount the grippinginsert is spaced apart is selected to cause the gripping insert to beinitially received more closely within the housing circumferentialinterior region, whereby the teeth of the gripping insert are initiallyconcealed in the housing circumferential interior region so that theplacement of the spacer in the gripping insert prevents the insert frommaking detrimental contact with the outer working surface of the mandrelduring the belling operations.
 6. The method of claim 3, wherein thespacer is left in position during storage of the belled pipe end but isremoved before pipe assembly in order to activate the sealing ring,companion ring shaped housing, and ring shaped gripping insert.
 7. Themethod of claim 1, wherein the gripping insert exterior surface has asloping profile which contacts a mating interior region of the housing,whereby contact with the exterior surface of a mating male plastic pipecauses the gripping insert to ride along the male surface at an anglewhile the row of gripping teeth on the gripping insert internal surfaceengage the exterior surface of the mating male plastic pipe.
 8. Themethod of claim 7, wherein the housing has a rear wall region which issubstantially perpendicular to a longitudinal axis of the female pipe,the rear wall region being in contact with the elastomeric body of thesealing ring as a mating male pipe is inserted into a mouth opening ofthe female plastic pipe, and wherein the housing exterior terminates ina tip region adjacent the rear wall region, the tip region serving tocover a portion of the companion sealing ring during belling operations.9. The method of claim 7, wherein the housing exterior surface has atleast one row of biting teeth for biting into an internal diameter ofthe female plastic pipe, the biting teeth being located on a region ofthe exterior surface which is forward of a vertical central axis of thehousing.
 10. The method of claim 1, wherein the housing is formed of amaterial selected from the group consisting of metals, composites andrigid elastomers or plastics.
 11. The method of claim 1, wherein thesealing ring is formed from a material selected from the groupconsisting of natural and synthetic rubbers and elastomers, polymericplastics and composites.